Light sources used in traffic and navigational control are generally point or near-point sources. Common examples are traffic semaphores and hazard lights commonly placed around road construction areas.
More recently line sources have become useful in traffic control applications. One such line source is taught by U.S. Pat. No. 5,043,850 (Dreyer, Jr.), commonly assigned herewith. According to the light source taught by that patent, a light conduit of the type taught by U.S. Pat. No. 4,805,984 (Cobb, Jr.) is utilized. Two lamps, differing in at least one optical property, are positioned in containers called lighthouses such that light is inserted into each end of the light conduit. The light is emitted from the conduit in directions such that the light will appear brightest to a person looking along the conduit. If the optical property that differs is color, a person looking one direction along the conduit will see a different color than a person looking the other direction.
A related type of product is produced when only a single lamp is utilized. When such a structure is constructed, the line source will be visible to a person looking along the light conduit in a direction toward the light source, but will not be readily apparent to a person looking along the light conduit away from the light source.
A problem that arises in such line light sources, both unidirectional and bidirectional, arises from the fact that the light sources utilizing parabolic reflectors are not perfectly collimated. Most of the light wall fall inside a directional cone that is acceptable, but some will be directed outside of that cone. That light outside of the preferred cone, which can be described as highly uncollimated, light will escape the tube very close to the insertion end of the tube. This is because it will undergo significantly more collisions with the walls of the light conduit. With each collision a percentage will escape the conduit and the remainder will be reflected and guided along the tube. In addition, the light emitted within the preferred directional cone will contribute illumination in an amount that is relatively constant over the entire length of the conduit. This will cause the line light source to be very bright at the insertion end and then to be relatively uniform in brightness over the remainder of the tube. A more uniform brightness would be desirable.